Freezing XPS characterization method of liquid-solid interface

Abstract

The invention discloses a freezing XPS characterization method of a liquid-solid interface. The method comprises the following steps: (1) taking a thin-layer two-dimensional material as a solid phase, transferring the solid phase into a liquid-phase sample, fishing out the solid phase by using an aluminum oxide substrate, forming a layer of liquid film of the liquid-phase sample between the aluminum oxide substrate and the solid phase at the moment, and constructing a liquid-solid interface sample; and (2) fixing a liquid-solid interface sample on a sample support, freezing in liquid nitrogen, freezing and solidifying the liquid-phase sample, putting the frozen and solidified liquid-phase sample into a sample introduction cavity, vacuumizing, then transferring the frozen and solidified liquid-phase sample into a test cavity for testing, and etching a solid phase by using an ion beam etching technology until the liquid-solid interface of the solid phase and the liquid-phase sample is detected, thereby realizing the XPS characterization of the liquid-solid interface. The liquid sample is frozen and solidified in a liquid nitrogen cooling mode, the vacuum requirement of XPS characterization can be met, and characterization of information such as components and valence states of the liquid sample in the ultrahigh vacuum environment is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of liquid-solid interface characterization, and in particular to a cryo-XPS characterization method for a liquid-solid interface. Background Art

[0002] At present, the research and development of new materials is a hot topic in the field of materials science, and the research objects involve materials science, life science, nanoscience, catalysis, etc. In these studies, in addition to the need to characterize many solid substances, substances with certain volatility or instability in vacuum, such as liquid samples, will also be involved. X-ray photoelectron spectroscopy (XPS) technology can provide information on the elemental composition, chemical state, molecular structure, chemical bonds, etc. of various compounds, thereby providing an important basis for studying the structure-activity relationship, controllable design and functional development of materials. XPS is generally used for surface analysis of solid samples, but in view of the need to ensure an ultra-high vacuum environment during the test process, it is usually required that the sample to be tested is fully dried, not easy to volatilize or contain volatile solvents, not easy to deliquesce or contain crystal water, etc. For non-conventional samples and liquids with certain volatility or instability in vacuum, such as organic small molecule materials, metal organic complex materials and organic electrolytes, it is generally difficult to perform XPS testing. Further, the characterization of liquid-solid interfaces (except ionic liquids) is more challenging. First of all, it is incompatible with vacuum. If conventional sampling methods are used, it will cause certain damage to the vacuum chamber of the instrument. Secondly, surface-sensitive XPS characterization techniques have difficulty in directly detecting the embedded liquid-solid interface. Summary of the invention

[0003] Based on the above background technology, the purpose of the present invention is to provide a cryo-XPS characterization method for liquid-solid interface, which can overcome the vacuum incompatibility problem of liquid samples, and by combining the ion beam etching method, the liquid-solid interface can be deeply analyzed to achieve XPS characterization of the embedded liquid-solid interface.

[0004] In order to achieve the above object, the technical solution of the present invention is as follows:

[0005] A cryo-XPS characterization method for a liquid-solid interface, the method comprising the following steps:

[0006] (1) Using a thin layer of two-dimensional material as the solid phase, the solid phase is transferred to a liquid phase sample, and the solid phase is picked up using an aluminum oxide (Al2O3) substrate. At this time, a liquid film of the liquid phase sample is formed between the aluminum oxide substrate and the solid phase to construct a liquid-solid interface sample;

[0007] (2) The liquid-solid interface sample is fixed on the sample holder and frozen in liquid nitrogen. After the liquid phase sample is frozen and solidified, it is placed in the sampling chamber and evacuated. It is then transferred to the test chamber for testing. The solid phase is etched using ion beam etching technology until the liquid-solid interface of the solid and liquid phase samples is detected, thereby achieving XPS characterization of the liquid-solid interface.

[0008] In the above technical solution, further, in step (1), the thickness of the solid phase is less than 100 nm.

[0009] In the above technical solution, further, in step (1), the solid phase material includes any one of graphene, boron nitride (BN), molybdenum disulfide (MoS2), tungsten disulfide (WS2), molybdenum diselenide (MoSe2), tungsten diselenide (WSe2), and MXene.

[0010] In the above technical solution, further, in step (2), the parameters of the ion beam etching are: ion source: Ar + , Energy: 3KV, Etching area: 2mm×2mm square.

[0011] In the above technical solution, further, in step (2), the injection chamber and the test chamber are both precooled, and the precooling time is 60 minutes.

[0012] The present invention first constructs a liquid-solid interface sample without surface contamination. Its ultra-thin cover layer can not only wrap the liquid to be characterized, but also be easily etched by ion beam, thereby exposing the liquid-solid interface below; secondly, the sample holder is cooled by adding liquid nitrogen, and the sample is etched by ion beam (Ar + The solid phase is etched by ion beam and gas cluster ion beam) etching technology to obtain a liquid-solid interface.

[0013] The beneficial effects of the present invention are:

[0014] (1) The present invention utilizes liquid nitrogen cooling to freeze and solidify the liquid sample, which can meet the vacuum requirements of XPS characterization and achieve characterization of information such as the composition and valence state of the liquid sample in an ultra-high vacuum environment.

[0015] (2) The liquid-solid interface sample without surface contamination suitable for frozen surface characterization constructed by the present invention has an ultra-thin covering layer that can not only wrap the liquid to be characterized, but also be easily etched to expose the liquid-solid interface underneath.

[0016] (3) The present invention uses cryo-XPS combined with ion beam etching to characterize the embedded liquid-solid interface, which is suitable for the characterization of liquid-solid interfaces in various systems. The surface-sensitive XPS characterization combined with ion beam etching can perform in-depth analysis of the frozen liquid-solid interface to obtain information such as the structure and chemical composition of the interface. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The schematic diagram and physical picture of the liquid-solid interface sample constructed in Example 1, a is a schematic diagram of the constructed liquid-solid interface sample, b is a photo of the sample in a frozen state, and c is a photo of Ar + Photo of the sample after ion beam etching test;

[0018] Figure 2 The liquid-solid interface sample constructed in Example 1 was heated to 400 °C in Ar + XPS spectra during ion beam etching. DETAILED DESCRIPTION

[0019] The present invention is described in detail below by way of examples, but the scope of the claims of the present invention is not limited by these examples. Meanwhile, the examples only provide partial conditions for achieving this purpose, and do not mean that these conditions must be met to achieve this purpose.

[0020] Example 1

[0021] The CVD-grown ~10 nm graphene / copper foil sample was etched in a 0.1 M ammonium persulfate solution to remove the copper substrate and obtain a self-supporting graphene; the graphene was transferred to water for cleaning, and then transferred to a 0.1 M KCl aqueous solution; it was then picked up with an aluminum oxide (Al2O3) substrate, at which time a layer of KCl aqueous solution liquid film was formed between the aluminum oxide substrate and the graphene, thereby constructing a graphene-covered 0.1 M KCl aqueous solution liquid-solid interface sample, as shown in FIG. Figure 1 shown.

[0022] The liquid-solid interface sample was placed directly in liquid nitrogen for 3 minutes for rapid freezing, and then the sample was quickly placed in a pre-cooled 60-min, sample stage temperature -120°C sample chamber to evacuate, and finally transferred to the main chamber for testing, which was pre-cooled 60-min and sample stage temperature -120°C; 3kV energy was used, and the etching area was 2×2mm 2 Ar + Graphene was etched under ion beam etching conditions, and the cryo-XPS test results were as follows: Figure 2As shown, each spectral line represents the XPS spectrum after etching for 2 minutes. In the initial spectrum (0min), the presence of the O 1s peak indicates that there may be oxidation on the graphene surface. After etching for 2 minutes, the O 1s peak disappears, indicating that the oxide layer on the graphene surface is cleaned. The C1s peak at this time comes from graphene. After etching for about 8 minutes (i.e., the 5th spectral line), O1s, K 2p and Cl 2p signals begin to appear, indicating that XPS can detect the KCl aqueous solution at the liquid-solid interface. After etching for 14 minutes (the 8th spectral line), the C 1s peak completely disappears, indicating that the graphene has been completely etched at this time. After etching for 24 minutes, the Al2p peak still does not appear, indicating that the aluminum oxide substrate has not been etched. This also shows that the O1s peak is completely derived from H2O without interference from the aluminum oxide substrate, thereby achieving the characterization of the liquid-solid interface.

[0023] The above examples can prove that the freezing method can freeze and solidify the aqueous solution and stably store it in an ultra-high vacuum environment. In addition, the surface-sensitive XPS characterization combined with the ion beam etching method can perform in-depth analysis of the frozen liquid-solid interface to obtain information such as the structure and chemical composition of the interface.

[0024] The above embodiments are only preferred embodiments of the present invention and are not intended to limit the implementation methods. The protection scope of the present invention shall be subject to the scope defined in the claims. Other different forms of changes or modifications may be made based on the above description. Obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A cryo-XPS characterization method for liquid-solid interface, characterized in that: The method comprises the following steps: (1) Using a thin layer of two-dimensional material as the solid phase, the solid phase is transferred to a liquid phase sample, and the solid phase is picked up with an alumina substrate. At this time, a liquid film of the liquid phase sample is formed between the alumina substrate and the solid phase to construct a liquid-solid interface sample; (2) The liquid-solid interface sample is fixed on the sample holder and frozen in liquid nitrogen. After the liquid phase sample is frozen and solidified, it is placed in the sampling chamber and evacuated. It is then transferred to the test chamber for testing. The solid phase is etched using ion beam etching technology until the liquid-solid interface of the solid and liquid phase samples is detected, thereby achieving XPS characterization of the liquid-solid interface.

2. The cryo-XPS characterization method according to claim 1, characterized in that: In step (1), the thickness of the solid phase is less than 100 nm.

3. The cryo-XPS characterization method according to claim 1, characterized in that: In step (1), the solid phase material includes any one of graphene, boron nitride, molybdenum disulfide, tungsten disulfide, molybdenum diselenide, tungsten diselenide, and MXene.

4. The cryo-XPS characterization method according to claim 1, characterized in that: In step (2), the parameters of the ion beam etching are: ion source: Ar + , Energy: 3KV, Etching area: 2mm×2mm square.

5. The cryo-XPS characterization method according to claim 1, characterized in that: In step (2), the injection chamber and the test chamber are both precooled, and the precooling time is 60 minutes.

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